Theoretical calculations of semiconductor heterojunction discontinuities

We have performed self-consistent density functional calculations on semiconductor heterojunctions, using ab initio nonlocal pseudopotentials, and have derived valence band discontinuities for many different interfaces between both lattice-matched and strained epitaxial layers. The agreement with reported experimental values is very reasonable. Based on the information obtained from the interface calculations, we have developed a new and simple approach to derive band discontinuities. In this scheme, the lineup of potentials between two materials is determined by the difference in average potentials which are calculated for a ‘‘model solid’’ consisting of neutral, spherical atoms. Band structures for the bulk solid are then aligned according to these average potential positions. This is a valuable ansatz which, for many cases, yields results close to those obtained from full self-consistent interface calculations. We also discuss examples, such as polar interfaces, where this simple ansatz is not sufficient.